Optical imaging is an emerging technology with potential for improving disease prevention, diagnosis, and treatment at the scene of an emergency, in the medical office, at the bedside, or in the operating room. Optical imaging technologies can noninvasively differentiate among tissues, and between native tissues and tissue labeled with either endogenous or exogenous contrast media, measuring their different photon absorption or scattering profiles at different wavelengths. Such photon absorption and scattering differences offers potential for providing specific tissue contrasts, and enables studying functional and molecular level activities that are the basis for health and disease.